These working models show the development of the heart of the clock - the escapement,
remontoire, pendulum balances and the basics of the going train. It's important to note
that while we borrowed liberally from Harrison's H1 design for our pendulum balances and
grasshopper escapement, we went several steps further. Harrison's escapement operated on
one wheel ours doubled it to two counter-rotating escape wheels; each driven by it's
own pendulum and remontoire connected through a differential system. The type of
remontoire we used is Wagner's swinging-frame concept, again never before used in a tandem
design. The inspiration for the double remontoire was a tower clock by Cooke & Sons in
the Royal palace Courts of Justice, England. However, that remontoire is mediated by a
cam, not a differential and is not a true swinging frame design. I also chose to double
Harrison's one second 'tick' to two, giving a slower, more hypnotic pendulum effect. This
also had the fortuitous advantage of helping our movement conserve the drop necessary for
an eight day duration. The idea is to maximize the visual effect of the counter-rotating
escape wheels. A design drawing is here. The
multiple cocks needed to support the remontoire was eventually cut in half.
These are the first videos taken by the Buchanan
firm in April 2006. They document the design and creation of the basic
elements of the going train for the astronomical skeleton clock. The main
components are: Dual compound pendulums, splitting differential to
alternately power a pair of Wagner gravity remontoire. These, in turn drive
a pair of counter-rotating grasshopper escapements. Notice how the
bird-design was envisioned for the escapements right from the beginning.
Other components are drive gearing from the weight barrel.
Escapement: The counter-rotating escape wheels will have the spokes
cut so as to provide a kaleidoscope effect. In this shot the spokes are painted on a clear
plastic toothed disk in black. The system has not yet been adjusted to get the spokes to
precess. The escapement pallets have graceful curvilinear parts and are designed to
maximize movement and visual impact. These will be jeweled in the manufactured version.
Movement overview: Notice that the pendulum balances have a cycle of 4
seconds versus the more common 2 second cycle as was used in Harrison's H1 and most of all
the later versions based on this design. I think that the slower rate is more hypnotic and
not quite so distracting as the faster cycle. A fortuitous side effect is the fact that
the entire train runs twice as slow reducing wear and, most importantly, alleviating the
critical issue of sufficient drop for an eight day duration. Here the escapement spokes do
Remontoire differential: One can see the differential at the center of
the picture move slightly as the remontoire cage is raised and lowered. This differential
powers both remontoire sequentially, as each drives it's individual escape wheel which, in
turn, are mediated by their individual pendulum balance. The system stays in synch because
the balances themselves, as in the H1, are slaved together.
Dual Wagner swinging frame remontoire: Each
alternatively rises and lowers and this is accomplished through the
remontoire differential above. The idea was inspired by a tower clock
serviced by Buchanan and later seen by me when I visited him before his move
from England in 2005. It was located at the Royal Courts of Justice, it was
a Dennison gravity escapement made by Gillett and Johnston and also equipped
with a dual remontoire based partially on Wagner's design.
The control of the remontoire's
movements relative to each other was done by a cam system in the Gillett vs.
a splitting differential used in this clock. This makes the alternative
rising and lowering of the remontoire cage pairs operate a bit differently
between the two designs. Gillett has what in my opinion, is a better look,
where one cage descends while the other remains stationary in its raised
position until the other has reached it's lowest point of decent, then the
upper one begins decent as the other rises to it's apex and remains there
until the cycle repeats. See video below.